On July 20, 2007, at 1100 central daylight time, a single-engine Lister Rotorway 162F experimental helicopter, N888TD, was substantially damaged during a forced landing to a field following a reported loss of engine power near Stratford, Oklahoma. The commercial pilot, sole occupant of the helicopter, was not injured. The helicopter was registered to and operated by the pilot. No flight plan was filed for the local flight that departed from the pilot's backyard near Stratford, Oklahoma, at 1045. Visual meteorological conditions prevailed for the personal flight conducted under 14 Code of Federal Regulations Part 91. According to the pilot, the helicopter was in cruise flight at an altitude of approximately 1,000-feet, at an estimated airspeed between 70 and 100 knots, when "the helicopter suddenly yawed to the right." The pilot added that he immediately and simultaneously applied left torque pedal to stop the yaw, lowered the collective, and entered an autorotation into the wind, at an airspeed of 70 knots. The pilot landed the helicopter in an "uneven" field, and the helicopter rolled, coming to rest on its left side. The pilot further stated that there were no warnings prior to or during the loss of engine power and there had been no recent mechanical problems with the helicopter. A review of photographs of the damaged helicopter revealed that the main rotors were twisted, the left landing gear skid was displaced inward, a tail rotor blade had separated, and the tail boom skin was wrinkled. The pilot reported that he had a total of 10 gallons of fuel on board at the time he departed and there was a small fuel spill at the accident site. Additionally, the pilot reported that he was the builder of the helicopter and the Federal Aviation Administration (FAA) had issued an airworthiness certificate in January/February 2007. At the time of the accident, the helicopter had accrued a total of 60.6 hours. Examination of the engine by the pilot revealed that the supercharger had seized, which resulted in the loss of power. The pilot reported having accumulated a total of 5,770-flight hours, of which 780-hours were in helicopters, with 60.6-hours in the same make and model. Weather at the Ada Municipal Airport (ADH), near Ada, Oklahoma, located about 16-miles east of the accident site, at 1110, was reported as calm wind, visibility 10 statue miles, scattered clouds at 2,300 feet, scattered clouds at 2,900 feet, temperature 84 degrees Fahrenheit, dewpoint 71 degrees Fahrenheit, and a barometric pressure setting of 30.06 inches of Mercury. The weather report included a remark of lightning south of the airport.